The invention relates to an internal combustion engine with an exhaust gas turbocharger and an exhaust gas recirculation device. Preferred embodiments of the invention relate to an internal combustion engine having an exhaust gas turbocharger and an exhaust gas recirculation device, whereby the internal combustion engine has a plurality of cylinders and each cylinder of the internal combustion engine has at least one intake valve and at least one outlet valve, and a compressor of the exhaust gas turbocharger is assigned to an inlet and an asymmetrical exhaust gas turbine of the exhaust gas turbocharger is assigned to an outlet of the internal combustion engine, the compressor is connected to the inlet via a charge air line, the exhaust gas turbine has two intake ports with different flow cross sections which are separated from one another by means of a partition and each inflow channel is connected to the outlet through its own exhaust gas inlet line whereby each exhaust gas inlet line is assigned a partial number of cylinders of the internal combustion engine and an exhaust gas recirculation line leads from the exhaust gas inlet line of the intake port having the smaller flow cross section to the charge air line.
There are known supercharged internal combustion engines, in particular diesel engines, which are equipped with an exhaust gas recirculation device to improve exhaust performance. The exhaust gas recirculation by means of the exhaust gas recirculation device serves in particular to reduce NOx emissions. These internal combustion engines have an exhaust gas turbocharger whose compressor is assigned to an inlet and whose exhaust gas turbine is assigned to an outlet of the internal combustion engine. The exhaust gas turbine and the outlet are connected by at least one exhaust gas inlet line from which an exhaust gas recirculation line of the exhaust gas recirculation device branches off. The exhaust gas recirculation line opens into a charge air line which connects the compressor to the inlet. An exhaust gas recirculation valve with which the exhaust gas recirculation is controllable is provided in the exhaust gas recirculation line.
U.S. Pat. No. 4,179,892 (corresponding German Patent DE 28 5 687 C2) describes an internal combustion engine in which the exhaust gas turbine has two separate intake ports (referred to as scroll channels in this publication) and an exhaust gas inlet line (referred to in the publication as an exhaust gas line) is assigned to each intake port. The exhaust gas inlet lines connect the intake ports to the outlet of the internal combustion engine. Each exhaust gas inlet line is connected separately from the others to a partial number of cylinders of the internal combustion engine. The intake ports have different flow cross sections. The exhaust gas recirculation line branches off from the exhaust gas inlet line which is assigned to the intake port having the smaller flow cross section. The flow cross section of the intake port and/or the exhaust gas inlet line is advantageously selected to be so small that there is a negative purging gradient so that at least a portion of the exhaust flows through the exhaust gas recirculation line into the charge air line. The recirculated exhaust is distributed uniformly among the cylinders.
The negative purging gradient results in an inferior purging and/or an increase in an internal exhaust gas recirculation of the cylinders which supply the exhaust gas recirculation device.
It has been found that with a uniform distribution of the recirculated exhaust gas to all the cylinders of the internal combustion engine, the exhaust gases of the cylinders supplying the exhaust gas recirculation device have a lower NOx concentration and a higher CO concentration in the exhaust than do the cylinders which do not supply the exhaust gas recirculation device. The higher CO concentration is an indicator of a low λ value, which is reflected in an increased output of carbon black and/or particles in diesel engine combustion.
An object of the present invention is to make available an internal combustion engine of the type referred to above so that its emissions are distributed uniformly over all the cylinders of the internal combustion engine.
This object is achieved according to certain preferred embodiments of the invention by providing an internal combustion engine having an exhaust gas turbocharger and an exhaust gas recirculation device, whereby the internal combustion engine has a plurality of cylinders and each cylinder of the internal combustion engine has at least one intake valve and at least one outlet valve, and a compressor of the exhaust gas turbocharger is assigned to an inlet and an asymmetrical exhaust gas turbine of the exhaust gas turbocharger is assigned to an outlet of the internal combustion engine, the compressor is connected to the inlet via a charge air line, the exhaust gas turbine has two intake ports with different flow cross sections which are separated from one another by means of a partition and each inflow channel is connected to the outlet through its own exhaust gas inlet line whereby each exhaust gas inlet line is assigned a partial number of cylinders of the internal combustion engine and an exhaust gas recirculation line leads from the exhaust gas inlet line of the intake port having the smaller flow cross section to the charge air line, wherein a control unit is provided to control the valve control times of the intake valves and/or the outlet valves of the individual cylinders of the internal combustion engine differently whereby the cylinders supplying the exhaust gas recirculation device have shorter valve overlap times or none at all in comparison with the cylinders not supplying the exhaust gas recirculation device.
Preferred embodiments of the inventive internal combustion engine are characterized by the valve control times of the intake valves and/or the outlet valves of the individual cylinders of the internal combustion engine which are provided differently, whereby the cylinders supplying the exhaust gas recirculation device have shorter valve overlap times or none at all in comparison with the cylinders that do not supply the exhaust gas recirculation device. The internal combustion engine has an exhaust gas turbocharger having an asymmetrical exhaust gas turbine. The asymmetrical exhaust gas turbine has two intake ports which have a different flow cross section. One flow cross section is selected to be so small that it results in a negative flow gradient on the partial number of cylinders that are connected to the intake port having the smaller flow cross section. The exhaust gas of this cylinder can thereby be recirculated via an exhaust gas recirculation device. The valve control times of the intake valves and the outlet valves usually have a valve overlap in internal combustion engines, i.e., the inlet opens before the outlet closes. Due to the valve overlap, there is internal exhaust gas recirculation in particular when there is a negative purging gradient. When the inlet is opened, the pressure in the cylinder space drops below the exhaust gas pressure and exhaust remains in the cylinder space or flows out of the outlet and back (internal exhaust gas recirculation). The degree of internal exhaust gas recirculation can be influenced with the design of the valve overlap times and can be shortened to advantage. This makes it possible to keep the NOx emissions at a required level while at the same time lowering CO emissions which is reflected in reduced carbon black and particulate emissions.
Advantageous refinements of and improvements on the above discussed preferred embodiment of an internal combustion engine are described herein and in the claims.
In certain preferred embodiments of this invention, the valve control times of the intake valves of the cylinders supplying the exhaust gas recirculation device are retarded. Advantageously the retarding of the valve control times is performed with a uniform valve lift diagram by five degrees of crank angle in the retarded direction.
In certain other preferred embodiments of this invention, the recirculated exhaust is divided in different ratios among the individual cylinders of the internal combustion engine, with a partial number of the cylinders of the internal combustion engine receiving all or most of the recirculated exhaust gas while the remaining cylinders receive the smallest amount of the recirculated exhaust gas or none at all. The ratio of the charge air required for combustion and the exhaust gas recirculated from the internal exhaust gas recirculation by means of the exhaust gas recirculation device can be balanced out among the cylinders of the internal combustion engine.
In certain other preferred embodiments of this invention, the cylinders that do not supply the exhaust gas recirculation device receive the largest amount or all of the recirculated exhaust and the cylinders supplying the exhaust gas recirculation device receive the smallest amount or none of the recirculated exhaust. In an expedient embodiment of this division, the cylinders not supplying the exhaust gas recirculation device receive a 70% portion of the exhaust recirculated via the exhaust gas recirculation device. The cylinders supplying the exhaust gas recirculation device receive a 30% share accordingly.
In certain other preferred embodiments of this invention the internal combustion engine is designed in the form of an in-line design with four or six cylinders, whereby the partial number of cylinders not supplying the exhaust gas recirculation device amounts to at least half of the cylinders of the internal combustion engine. Due to the negative purging gradient on the cylinders supplying the exhaust gas recirculation device, the efficiency drops because of the inferior purging of the cylinders. The loss of efficiency can be compensated by optimized charge alternation of the cylinders that do not supply the exhaust gas recirculation device. In order to avoid a negative effect on the overall efficiency of the internal combustion engine, the partial number of cylinders supplying the exhaust gas recirculation device is limited to at most half of the cylinders of the internal combustion engine.
In certain other preferred embodiments of this invention, an exhaust gas recirculation valve in the form of a throttle valve is provided in the exhaust gas recirculation line. The exhaust gas recirculation valve is controllable by means of a signal line by a control unit of the internal combustion engine. Thus the exhaust gas recirculation is controllable by means of the exhaust gas recirculation device and is adaptable to an engine characteristics map of the internal combustion engine.
Additional features and combinations of features are derived from the description and the drawing. A concrete exemplary embodiment of this invention is shown in simplified form in a drawing and explained in greater detail in the following description.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.